| Network state estimation is the base of power system dispatching automation. The art of network state estimation is becoming mature at theoretical and practical aspect while along with the development of SCADA.To a certain extent, the power system has rounded into the era of automation. However, with the emergence of the wide area measurement technology based on GPS, the promotion of energy conservation and emission reduction policies as well as the continual improvements of the requirement for the ability of power electric system to resist perturbations, the network state estimation has to face the new problems in all aspects, such as research on the relationship between the existing network state estimation and phasor measurement unit(PMU),the contribution of PMU to network state estimation, the mixed algorithm with PMU, the generalized network estimation including analog and digital measurements, parameters as well as characteristic values that accompany with the dynamic thermal rating and electric power equipment condition-based maintenance. Against this background, the network state estimation and its expansions has been studied. The main works and achievements can be summarized as follows:(1) The impact of PMU on traditional state estimation based solely on the SCADA system is studied and analyzed. An appropriate solution is proposed to improve the power system state estimation theory. PMU can directly get the measurements of bus voltage phasors. In that way, the state variables of system (the bus voltage magnitude and phase angle) are known. Compared with the SCADA measurement, the PMU measurement is the explicit function of state variables, while the latter is the implicit function. State estimation based on SCADA system can run on the conditions that the whole system is observable, but PMU can make the network state observable locally. Obviously, if the PMU measurement accuracy is high enough and can make the whole network state observable completely, the state estimation will be no longer needed. If PMU measurement accuracy is high enough but only allocated at part of power system, the network state estimation based on SCADA would be simple. For the latter, this thesis tried to explore the impact of PMU on the network state estimation such as observabilty analysis, algorithm research as well as bad data identification. Firstly, due to the introduction of PMU, the traditional observability analysis methods obtain a significant simplification. The more PMU measurements allocated, the easier the observabiltiy analysis will be. Secondly, under the assumption that PMU measurement has sufficient precision, the reduced state estimation model and algorithms based on SCADA can be presented to estimate the unknown state variables. And finally, against the reduced state estimation model, the impaction of PMU measurements on bad data identification methods has been discussed. It is found that the redundancy level is raised as the amount of PMU measurements increases. And the identification ability is enhanced. Furthermore, once the PMU measurement has error, the state variables from PMU need to be corrected, and the local mixed state estimation is proposed to improve the accuracy.(2) For the situation of the PMU and SCADA measurements co-exist, a decomposition and coordination state estimation algorithm is presented. Local estimation can be processed with the help of PMU measurements, and the system can be divided automatically into a number of observable subsystems around PMU. Based on this idea, this thesis proposes a decomposition and coordination state estimation algorithm in view of quicker calculating speed. Decomposition relies on the location of PMU, while coordination is responsible for linking different sub-systems smoothly and unifying the result at the same reference bus angle. In short, quicker speed is achieved. The process is listed as follows:According to the configuration of PMU in the power system, the power system can be divided into two kinds of subsystem. The PMU observable island is a cut-set that formed by direct electrical connection of the PMU bus, while the SCADA observable island is cut-set containing only SCADA measurements and buses without PMU. In This way, The boundary bus is corresponding to the intersection of PMU observable island and the SCADA island, and connect element lies between the two. After the system is divided, all PMU observable islands are estimated and power flow on connect element is obtained. Then, taking into account the result as pseudo-measurements, the estimation is run on the SCADA observable islands. Finally, the angles of the reference bus and boundary buses in subsystems are coordinated to the unified solution with the same reference bus.(3) Under the guidance of the concept of generalized state estimation, a state estimation model and method is proposed to identifying closed switch element status. In order to identify the topology error related to closed switches, the concept of the virtual feature switch is put forward to build the minimum feature network, which does not affect the quality of the identification. In addition to analog measurements, zero-voltage-drop for virtual closed switch as equality constraint is added to formulate the model of state estimation which is solved as a nonlinear optimization problem with equality constraints. Then, on the condition that the analog measurements error probability distributions are known, the meaning of Lagrange multipliers is expressed, that is to say the Lagrange multiplier corresponds to the virtual zero-impedance component measurement equation, and Lagrange multiplier distribution has consistency and relevance with the residual distribution. The relation between residual and Lagrange multiplier is used to find error information of zero-impedance component. A unified reconignition of analog measurement and close switch is ultimately obtained. At same time, the thesis verifies that bad data identification of whether analog measurement or switch status is not confused with each other when there is only one bad data in the system. Because the model is build from virtual characteristic switches, the size of the calculation is effectively reduced and calculation speed is increased significantly, which means the method has a certain practical engineering prospects.(4) With concept of the state estimation, the temperature estimation model of the transmission line is established with PMU measurements and electro-thermal coordination equations of overhead transmission line, which provides real-time estimation theory of the transmission line temperature. The key idea is, among line parameters such as resistance, admittance and conductance etc, which only resistance will vary with the temperature. Under operating condition, real-time tracking of temperature can be indirectly achieved by resistance parameter estimation. If the terminals of transmission lines are equipped with PMU, the current and voltage phase of transmission line at both terminals are known. According to principles of electric engineering, measurement equations are formed in Cartesian coordinates. Then, the linear weighted least squares method is established on the transmission line resistance. Based on the rule of resistance and the temperature, the temperature tracking will be achieved by estimating the resistance of transmission line in real-time. When direct PMU measurements are converted to equivalent indirect measurements, the corresponding errors are converted too. By the known the probability distribution of directly measurements' errors, the distribution of indirect measurements'errors is deduced. The probability distribution of the performance index is also analyzed when measurements'errors are interrelated. The result shows that the performance index is still to meet the distribution of x2, which means that the traditional method of bad data identification is still valid. So, the model and method are simple and easy to realize, which provide a theoretical basis for fully exploiting the potential capacity of transmission lines.(5) On the basis of hardware of the dynamic thermal rating (DTR) technologies and combined with electro-thermal coordination (ETC) theory, the conception of soft-DTR is introduced. The model and algorithm of tracking transmission line rating are established from the SCADA information. The model and algorithm are fulfilled as follows:First, there is rich electrical information of the transmission line in power system, by which the extended estimation with transmission line resistance is established. Furthermore, in order to take full use of resistance prior information, considering the Markov properties of resistance changing, the current estimated value is amended and smoothed by the adjacent moment value, and the tracking accuracy is improved. The temperature of transmission line is obtained indirectly by the analytic relationship between resistance and the temperature. Then, a simplified heat balance differential equation (HBE) model of transmission lines is set up with time-varying environmental parameters. According to a continuous transmission line temperature series, the dynamic estimation of time-varying environmental parameters is realized by fading recursive least squares method. Then, complete functions of hardware DTR functions are achieved only by electrical measurements. Finally, in comparison with hard DTR technology, the trend of temperature is grasped by the line resistance indirectly, which means that the temperature accuracy is influenced by the resistance of transmission lines rather than the surrounding environmental conditions. The model and method are simple and easily implemented, and the soft-DTR of each transmission component can be realized as long as the estimation is workable.(6) Based on soft-DTR, the framework and platform of the project named "On-line evaluation system of the transmission components loadability at regional power grid" is designed, which provides a favorable basis for the whole system.Now it is applied in Yantai power grid of Shandong Province. In the operating conditions, the loadability of power transmission component is mainly constrained by operating conditions in the power system and itself physical condition. The project of "On-line evaluation system of the transmission components loadability at regional power grid" is to judge transmission components loadability mainly by the temperature for the scheduling and control decision-making.At the same time, the transmission efficiency of grid is improved and the resource is saved. The main functions of the project are listed as follows:Based on the soft-DTR, the temperature of transmission component is estimated, as well as the dynamic parameters of HBE. Then, electro-thermal coordination power flow is run with the temperature as extented state. Taking into account the thermal load constraints, voltage level constraints and static power angle stability constraints, the evaluation of the transmission line loadability is realized.The loadability margin is also analyzed. Under the anticipated events, the varying of the transmission component loadability is tracked, which provides decision support for scheduling and early warning. The foundation of the above-mentioned functions is state estimation. This thesis provides a platform based on state estimation with SCADA and PMU measurements. The algorithms include: the algorithm of state estimation with the identification of closed breakers information, state estimation including PMU, tracking estimation of transmission line temperature based on PMU or SCADA, tracking of transmission line dynamic thermal rating and so on. The platform not only provides technical support for the comprehensive evaluation of power transmission line, but also realizes the organic combination of the theory and practice.In conclusion, taking into account the PMU measurements, switch status, and state related with transmission line rating evaluation, the thesis has done comprehensive study and proposed the model and appropriate solutions. The study has been verified by the application at Yantai power grid in Shandong Province. A little progress has been made in this field. Of course, from the point view of prosperity, development and improvement, there are still a number of theoretical and practical issues remain to be explored and studied further.
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